Generalized multifrequency current controller for grid-connected converters with LCL filter

Abstract

This paper presents a grid-side current controller for grid-tied inverters with LCL filter, including harmonic current elimination. The proposed controller only measures the grid current and voltage and it combines excellent dynamic characteristics with good robustness. Contrarily to previously proposed harmonic-current controllers, the presented solution offers a generalized method that gives a consistent (with minimal variation in the reference-tracking dynamics) and stable performance irrespectively of the number of current harmonics to be canceled and of the resonant frequency of the LCL filter (provided that it is lower than the Nyquist frequency). The response to reference commands is completely damped and fast. The response speed is set in accordance with the low-pass characteristic of the LCL filter so as to limit the control effort. Concerning the disturbance rejection, the controller offers an infinite impedance to any disturbances (such as grid voltage harmonics) at a set of arbitrarily specified frequencies. This allows the designer to eliminate all the undesired current harmonics with a simple design process. In addition, the performance of the presented controller is evaluated in terms of a fundamental tradeoff that exists between robustness to variations in the grid impedance and the number of frequency components rejected. Finally, simulation and experimental results that validate the proposal are presented.